Marijuana use among adolescents is associated with a variety of negative health and psychosocial outcomes. The rapidly changing normative context surrounding marijuana use, however, raises significant challenges for prevention. To date, 20 states and the District of Columbia have legalized marijuana for medical use, 17 states have decriminalized marijuana possession, and two states have legalized marijuana for recreational use. Given the momentum towards normalization of marijuana use, new approaches are needed to intervene with youth to reduce marijuana use and risks associated with marijuana use. Aims: This feasibility study will develop an intervention, using a combination of traditional media and mobile technologies to reduce marijuana use among high school students by increasing knowledge and concern regarding high-risk use and raising awareness of the inconsistency of such behaviors with personal autonomy and agency. Specific aims are (1) adapting previously-tested marijuana communication approaches for use in high schools; (2) testing feasibility of use of smartphone technology to deliver appropriate messages proximate to time of behavioral decision; (3) conducting an efficacy test regarding potential of such a campaign to reduce the prevalence of use and quantity and frequency of marijuana use among high school students, via increasing knowledge and concern regarding high-risk use, and the inconsistency of such behaviors with personal autonomy; (4) assessing whether these approaches have a positive effect on alcohol-use related outcomes. Approach: We will conduct focus groups to develop the messages and materials for the intervention. Following message development, we will work collaboratively with Klein Buendel (KB), a multi-media development firm that specializes in mobile phone applications for public health interventions, to develop a smartphone app and text messaging platform. The intervention will be implemented in a total of six schools in the San Francisco Bay Area using a cross-over design. The California Healthy Kids Survey, a state-wide survey that allows custom questions, will occur in each school in Years 1 - 3 of the study, and will be used to assess the efficacy of the intervention. Following the implementation of the intervention in the schools, face-to- face interviews with school administrators will be conducted to ascertain their reactions to and experiences with the intervention. Innovation: This feasibility study will explore the use of smartphone technology and text messaging as a way to extend the effectiveness of traditional school-based media approaches and disseminate prevention messages to youths at a time and place proximal to behavioral decision regarding marijuana use. This media- based approach does not require classroom or teacher time, making it viable for widespread adoption in an era of growing demands for school academic performance and decreased available school resources for prevention. If successful, this feasibility study will provide the basis for a larger randomized tral.